Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO)

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To: Nick Copeland <nickycopeland@...>
Cc: linux-audio-dev@lists.linuxaudio.org <linux-audio-dev@...>, <jef@...>
Date: Tuesday, August 21, 2012 - 8:59 pm

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On Tue, 2012-08-21 at 22:14 +0200, Nick Copeland wrote:

d
,
-
e
s,

Yes, but as already mentioned, for a modular to be usable a standard is
required. The analog synths on which this was modeled have such a
standard. As it turns out, that was based around A as well, just dug up
by Robin Gareus on IRC:

https://en.wikipedia.org/wiki/CV/Gate

Even volts on A in both schemes.

> Consider the following points:

Erm... only being able to modify frequencies upwards would be useless.

Nobody is suggesting that *all* "voltages" that affect frequency are
absolute. Clearly modulation inputs would be centred about 0 relative
to... whatever/nothing. If you do otherwise, then you ruin the ability
to modulate frequency with anything (e.g. audio signals).

Plugging a e.g. keyboard frequency into an amplifier gain directly
(without any conversion) is obviously not going to work no matter how
you do things. Using audio to modulate frequency, however, is a
fundamental ability. You don't even need modulation inputs for this to
be useful, you can just plug the absolute frequency and some audio into
the same port (so they will be summed) and get the FM you expect.

Regardless, it has to be centered about something. If you want to make
it positive only, then it has to be rooted at something. To me it seems
all this achieves is limiting the frequency range you can express (since
you have to pick a lowest note) and gains nothing. If you divide 440 by
2 successively until you get close-ish to 0, you get numbers like
0.21484375. Centering about standard concert tuning frequency seems
quite a bit more sensible to me.

If you could start at 0Hz, that would be nice, but of course 0Hz * 2
is... 0Hz :)

>=20

Fons pointed this out, and while correct in some academic sense, it is
not useful. Pretending the absolute frequency signal is not in fact
absolute and moving the problem to the receiver doesn't really make the
problem go away, and in practice raises a ton of implementation
difficulties that weren't there before. Suffice to say it is highly
preferable to have *ports* be meaningful on their own.

In these modular synths, both analog and digital, signals at times *do*
represent absolute frequencies. This is a fact, this is reality, this
is not debatable. Yes, you can think of these as all modulation
frequencies and move the problem of a base frequency onto the modular
itself, which is reasonable in an academic sense, but not useful. It
makes the theoretical problem go away by way of semantic trickery only,
it doesn't make the actual problem go away. In reality you have some
'note' module which emits CV to describe frequency, which is inherently
absolute since describing a frequency is what it does. This means
everything needs to agree on what the base frequency is.

A good thing for plugins to do would be to have an input that defines
the center frequency in Hz, though these plugins do not have such inputs
and I'd rather not add ports to them (it is also a teeny bit more math
to do, but probably not a significant overhead)

> Just to be complete, I have no objection to such signals having some

Signals inherently have implied semantics at some point if they are ever
actually used to do something.

> There will be some apps that do not have such

No restrictions here. In most apps like this you are always free to
plug any signal into anything. The need to define these things is
essentially a documentation issue (for both humans and programs). It's
all just floats at the end of the day.

Thanks for the input,

-dr

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Messages in current thread:
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Jeff McClintock, (Mon Aug 20, 11:02 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Tue Aug 21, 12:50 am)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Nick Copeland, (Tue Aug 21, 8:14 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Fons Adriaensen, (Tue Aug 21, 9:54 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Tue Aug 21, 10:29 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Fons Adriaensen, (Tue Aug 21, 11:02 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Tue Aug 21, 11:50 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Thorsten Wilms, (Wed Aug 22, 8:30 am)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Wed Aug 22, 4:43 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Fons Adriaensen, (Wed Aug 22, 9:12 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Wed Aug 22, 9:32 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Fons Adriaensen, (Thu Aug 23, 10:56 am)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Thu Aug 23, 4:06 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Fons Adriaensen, (Thu Aug 23, 4:35 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Thu Aug 23, 5:07 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Wed Aug 22, 5:37 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Nick Copeland, (Wed Aug 22, 1:24 am)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Wed Aug 22, 1:57 am)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Tue Aug 21, 8:59 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Nick Copeland, (Tue Aug 21, 10:11 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), Jens M Andreasen, (Wed Aug 22, 3:50 pm)
Re: [LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO), David Robillard, (Tue Aug 21, 10:52 pm)